The outdoor unit and indoor unit of an air conditioner each generally include a heat exchanger for exchanging heat between the heat exchanger and the air surrounding it. A heat exchanger normally includes a plurality of cooling fins, a plurality of heat transfer lines, and air transport means such as a propeller fan or the like. The plurality of cooling fins are plate-shaped members that are disposed with a predetermined gap between each member in the plate thickness direction. The plurality of heat transfer lines are mounted such that they pass through the plurality of cooling fins in the plate thickness direction. The air transport means serves to transport an air flow to the plurality of cooling fins and heat transfer lines.
In this heat exchanger, heat exchange occurs by transporting an air flow with the air transport means through the gaps between adjacent cooling fins, and evaporating or condensing refrigerant that flows inside the heat transfer lines.
The cooling fins are generally composed of a pure aluminum plate material, and the plate material is manufactured by cutting the plate material into predetermined fin shapes by means of a metal die. Before the plate material is cut, a corrosion resistant coating is applied to the plate material to form a corrosion resistant film that will improve the corrosion resistance of the plate material.
However, rolling oil remains on the surface of the plate material because rolling oil is used to roll and manufacture the plate material. Because of this, when the coating is applied to the surface of the plate material, the coating will be repelled by the rolling oil and thus it will be difficult to apply the coating. Accordingly, in a conventional surface treatment, before the coating is applied, the plate material is dipped in a tank of alkaline solution in order to degrease the plate material, and is then dipped in a tank of a chromic acid processing agent in order to both form the corrosion resistant film on the surface thereof and roughen the surface thereof.
This conventional method of treating the surfaces of the plate material is quite expensive because of the need for processing tanks for the degreasing and chromic acid processes.
In addition, because the treatment waste fluid produced by the chromic acid process includes heavy metals and is a problem from an environmental point of view, it will be necessary to dispose of the treatment waste fluid after a predetermined number of treatments. However, when this waste fluid is processed, the running cost thereof is quite expensive because specialized waste fluid tanks must be treated differently, and because the waste fluid must be processed at fixed intervals of time.